Misfire Number 2 & 6 on 3rd drive cycle

Hello everyone I’m new to the forum and eager to learn. I have a 2002 jeep liberty 3.7 that starting throwing P0300,P0302 and P0306 with a flashing check engine light. By doing a hard reset by disconnecting the battery it will throw the codes again with flashing check engine light on the third drive cycle start up.

Little back history. Started burning coolant and found passenger side head was cracked between two and four. Replaced head and started having this issue. During diagnosis, I have swapped injectors, coil packs, new plugs were installed with head replacement and replaced injector connectors. I’ve tried a different pcm with the same outcome. I have done some research and from what I have learned is a hard misfire will shut the injector driver module down on misfiring cylinders. Fuel pressure test good per Mitchell pro demand. I have also removed front timing cover to verify timing is correct. I have not performed a compression check to verify compression, but vehicle runs strong and good with no misfires during drive cycle one and two. This leads me to believe that it is not a mechanical issue. I was thinking wiring, but I’m kind of lost at the fact it’s on the third drive cycle start up each and every time. I am hoping that somebody can enlighten me with something that I don’t know or give me a direction to look. Thank you in advance.

Have you checked the O2 sensor? I have recently read a post with those codes and it found out that downstream o2 sensor was not cycling well

Yes I swapped O2 sensor after head swap. Had same issue with old sensor and found it was bias. Figured that was the issue cat swapped as well for fear of coolant damage. I reposted this thread on discussions as when I first posted I wasn’t sure where to post.

I had those exact codes on my 2002 Liberty. It turned out to be thrown rockers due to worn out lash adjusters (lifters). Youtube has videos on removing the valve covers to check, and on how to replace the lash adjusters and rockers. Any play in a lash adjuster could allow the cam lobes to throw out the rocker due to a lack of oil, especially when the engine is cold and oil has drained back down to the oil pan. Original rockers had the oil hole pointed straight up. New design has the hole that squirts oil angled towards the lash adjuster to allow more oil to hit the lash adjusters. I'd definitely recommend getting the new design rockers as opposed to the original style.